Schematic for Hitachi KM-1520ZD needed

[philbar73]

I'm looking for the Schematic for a Hitachi KM-1520ZD radio. Can anyone help?

[Mikes Z car]

What is wrong with the radio?

[philbar73]

The radio works fine. I want to look at the output stage before I hook it up to a power amp so I don't damage it. I think its transform isolated but do not want to make a mistake.

[Mikes Z car]

Generally output stages that aren't transformer isolated use an electrolytic capacitor to do the isolation. I have never seen a car radio that used a transformer, all I have seen use an electrolytic capacitor. Is the impedance of the power amplifier on the connection that would go to the radio very low, like below 8 ohms?

KM-1520 Car Radio Hitachi Ltd.; Tokyo, build 1973, 4 picture

Edited September 25, 2013 by Mikes Z car

[philbar73]

The output (speaker leads) measure .9 ohms. The only thing I can think of is I'm testing a winding on a transformer. If it was a capacitor I would think that I would see the reading changing. It solid at .9 ohms in either direction. The white and black lead is tied to ground, the case of the radio.

When I connect the radio to the amp there is no output. If I lift the ground wire and just connect the white lead from the radio it works. I'm an electrical engineer and would like to understand what I'm dealing with. The power amp has a speaker level input but it seams the - input on the power amp will not work when grounded. I put a small audio transformer between the radio and the power amp to isolate the ground and it acts the same. I don't understand what's going on.